Paper receptacle

ABSTRACT

A paperboard material 101 is mainly composed of a paperboard having a weight of 200 to 450 g/m 2 , a density of 0.65 to 0.82 and a gas permeability of 50 to 200 sec. A first resin layer having liquid-impermeability and thermal resistance is formed entirely on the surface of the paperboard on the inner side of the receptacle, and a second resin layer having permeability to gas and liquid is formed entirely on the back surface of the paperboard. Radial score lines 117 are formed in the portion corresponding to the corners of the paperboard material 101 toward its outer periphery. The score lines 117 do not reach the outer periphery of the paperboard material 101 but terminate at the position at a distance &#34;a&#34; (1 to 3 mm). The score lines 117 are formed by pressing the paperboard with a pressing die from the side constituting the inner side of the receptacle toward the outer side.

TECHNICAL FIELD

The present invention relates to paper receptacles, and particularly toa paper receptacle with a curled periphery, paperboard (cardboard) usedas the material for the paper receptacle, a method for forming the paperreceptacle, and a machine for forming the paper receptacle.

BACKGROUND ART

Plastic receptacles made of synthetic resin such as polypropylene areconveniently used as lightweight and cost-effective receptacles forfoods. However, the plastic receptacles, though very convenient, have aproblem in destruction by fire. That is to say, the combustion calorieof synthetic resin is much larger than those of paper and the like andhence it generates a great amount of combustion heat for its bulk.Accordingly, temperature in the incinerator rises very high, which maydamage the incinerator or reduce its life time.

For the reasons above, demands for paper receptacles with low combustioncalorie are increasing these days, as substitutes for the plasticreceptacles. The table below shows a comparison of combustion caloriesbetween a paper receptacle and a plastic receptacle with the same bulk.

                  TABLE 1                                                         ______________________________________                                                                    Plastic                                                       Paper Receptacle                                                                              Receptacle                                        ______________________________________                                        Capacity    150 ml          the same                                          Size        110 mm square ×                                                                         the same                                                      27 mm high                                                        Material Area                                                                             220 cm.sup.2    the same                                          Material    Three-layers    polypropylene                                     Composition structure of:   sheet (500 μm)                                             polymethyl pentene                                                            (22 μm),                                                                   paperboard (390 μm),                                                       vinyl resin coat                                                              (2 μm)                                                         Combustion  33 Kcal/piece   110 Kcal/piece                                    Cal.                                                                          ______________________________________                                    

Values of physical properties of materials;

    ______________________________________                                                   Specific Combustion heating                                                   gravity (g/cc)                                                                         value (KCal/Kg)                                           ______________________________________                                        Paperboard   0.75       4,400                                                 polymethyl   0.83       11,000                                                pentene                                                                       Vinyl resin  1.40       4,500                                                 Polypropylene                                                                              0.91       11,000                                                ______________________________________                                    

As can be clearly seen from the comparison above, the heating value ofcombustion of a paper receptacle is about one-third, or smaller, of thatof a plastic one with the same bulk capacity.

FIG. 20 is a perspective view of a conventional rectangular paperreceptacle with a curled periphery.

Referring to the figure, the rectangular receptacle has a bottom 123,peripheral walls 119 and 121 turned upwardly at a certain angle from thefour sides of the bottom 123, peripheral corners 125 where theperipheral walls 119 and the peripheral walls 121 are connected, aflange 126 formed in the horizontal direction at the upper ends of theperipheral walls 119, 121 and the peripheral corners 125, and a curling127 formed around the outer periphery of the flange 126.

FIG. 21 is a diagram showing the appearance of a blanked paperboardmaterial for forming the receptacle shown in FIG. 20.

Referring to the figure, the paperboard material 101 is composed of arectangular sheet material with four rounded corners. The dotted lineshows the boundary corresponding to the bottom 123 of the formedreceptacle. The parts located above and below it correspond to theperipheral walls 121, whose peripheries form peripheral straightportions 103. The parts located on the right and left sides of thebottom 123 correspond to the peripheral walls 119, whose peripheriesform peripheral straight portions 105. As the parts corresponding to theperipheral corners 125, A score lines 117 are formed in the areas A tothe outer periphery on radii extending from the central positions of thecurved portions, 115a and 115b which are located in the bottom 123. Theedges of the peripheral corners 125 form the curved portions 109 likecircular arcs around the center positions 115a and 115b of the curvedportions. In this diagram, the areas A are subjected to drawing in dieforming or the like. The corners of the dotted line defining the bottom123 are defined by the arcs of concentric circles with respect to thecurved portions 109 around the centers 115a and 115b of the curvedportions.

FIG. 22 is a process diagram schematically showing, in sections, theprocess of forming the paper receptacle of FIG. 20 with a formingmachine using the paperboard material of FIG. 21.

The paperboard material 101 shown in (1) in the diagram is pressedbetween die members of the forming machine. Then the peripheral walls119, 121 and 125 of the formed receptacle are formed as shown in (2),whose margins form the flat portion 129.

Next, as shown in (3), the flat portion 129 is formed into thehorizontal flange portion 126 and an upstanding portion 133 for curling.Then as shown in (4), the upstanding portion 133 is curled and thus thecurling 127 is formed around the entire periphery.

As stated above, the conventional rectangular paper receptacle with acurled periphery is formed from a sheet of paperboard material. Althougha rectangular paper receptacle has been described as an example,circular receptacles are formed in the basically same way. In this case,the score lines are formed around the entire periphery of the paperboardmaterial.

The conventional paper receptacle described above, having its entireperiphery curled, is not sufficient as a receptacle when it is used as areceptacle with a cover or with protection film heat-sealed to protectits contents.

FIG. 23 is a cross-sectional view of the rectangular paper receptacle ofFIG. 20 provided with a cover plate.

Referring to the diagram, the periphery 151 of the cover 150 is bentdown to fit around the periphery of the curling 127 of the paperreceptacle. Accordingly, increasing strength of the fit of the coverrequires an increase of strength of the curling 127. As shown in FIG.21, however, the score lines 117 are formed to the outer edge of thepaperboard material 101, or to the part where the curling 127 is formed,and therefore the outer ends of the score lines 117 are intactly curled,resulting in reduction of the strength of the curling 127.

FIG. 24 is an end view of the main part of the rectangular paperreceptacle of FIG. 20 with protection film sealed with heat.

Referring to the diagram, synthetic resin film 151, composed of acomposite material of synthetic resin films of polypropylene,polyethylene, or the like, or of a composite material of paper oraluminum foil and a synthetic resin film or a heat-sealed material, isheat-sealed on the top surface of the flange 126 of the rectangularreceptacle. To provide good heat sealing, it is preferable to form thetop surface of the flange 126 smooth. However, particularly in the caseof a rectangular receptacle, the corner portions are apt to becorrugated in forming. This degrades the smoothness of the flange 126,which may cause inferior heat sealing.

Furthermore, recently, paper receptacles are used as easy heat-resistingreceptacles, heated in an oven or the like together with foods containedtherein. In such a case, the paper receptacle is formed by using apaperboard provided with heat-resisting resin coating or heat-resistingresin film (density: 0.85-0.90, permeability (by the testing methodbased on the English version of JIS P8117): 250-600 sec) on its innerside.

This publication specifies the testing method for the air permeabilityof paper and paperboard that permits 100 ml air to pass through an areaof 645 mm² in 2 to 1800 seconds. Such materials as crepe and corrugatedpapers of which clamping down cannot shut out its surface and edgeleakage, are excluded from the application of this standard.

The testing device is divided into two types, Types A and B, consistingof an outer cylinder partly filled with oil and an inner cylinder whichcan freely slide in the outer cylinder and having an open or closed top.In Type B, the cylinder is of concentric double cylinder construction,having an open top, containing the oil in itself, and the inner cylinderforms an air passage reaching the lower clamping plate. Air pressure forthe test is provided by the mass of the inner cylinder.

The testing device is of a construction capable of applying an airpressure onto the test piece held between the clamping plates having acircular orifice of 28.6±0.1 mm in diameter. The clamping plates mayform the top of the inner cylinder (in Type A) or may be mounted in thebase of the testing device (in Type B). (The latter construction isdisclosed as being preferable.) An elastic gasket is attached to theclamping plate on the side exposed to air pressure, and the test pieceis held in contact with the gasket when clamped for the test.

The gasket consists of a thin, elastic, oil-resistant, nonoxidizingmaterial having a smooth surface and capable of preventing air fromleaking through the test piece and the clamping plate. An oil-resistantrubber, such as grade S.T. Thiokol gasket of 0.77 mm in thickness, andof 50 to 60 in Durometer hardness, is disclosed as being a satisfactorygasket material. The inside diameter of the gasket is 28.6 mm and theoutside diameter 34.9 mm. The bolt holes in the gasket are centeredexactly to those in the clamping plate, and, in order to align andprotect the gasket in use, it is cemented with shellac into a groovemachined in the clamping plate. This groove is concentric with theaperture in the opposite orifice plate, and 28.4 mm in inside diameter,35.2 mm in outside diameter and 0.5 mm in depth for convenience ininserting and attaching the gasket. The outer cylinder is 254 mm highand has an internal diameter of 82.5 mm, and marked with a level line at127 mm from the inner bottom.

The outer cylinder is equipped with four bars, each 190 mm in length,2.4 mm in width and 2.4 mm in thickness, on the inner surface to act asguide tracks for the inner cylinder. The inner cylinder is graduated inunits of 50 ml, and has a total range of 350 ml. It is 254 mm high, andhas an external diameter of 76.2 mm, an internal diameter of 74 mm and amass of 567±1.0 g. Or, the inner cylinder may be graduated in units of25 ml for the first 100 ml and have a range of 400 ml.

The oil used in the testing device is a lubricating oil having 60 to 70seconds Saybolt Universal viscosity at 37.8° C. {10 to 13 mm² /s} and aflash point of not less than 135° C.

The publication discloses that a light spindle oil is suitable for thispurpose. Oil is used in preference to water, because it does not affectthe moisture content of the sample nor does it affect the aluminum innercylinder. The oil does not contain any essential oil or easily volatileoil.

The device is tested for air leakage by clamping a thin piece of smooth,hard-surface airtight material, such as metal foil or cellophane,clamped between the orifice plates. The leakage should not exceed 50 mlin 5 h.

The test piece is approximately 50×130 mm in size. Test pieces of notless than 50×50 mm may be used in the device having the clamp in thebase.

Test pieces are conditioned prior to testing.

The testing device is placed on a level surface so that the innercylinder becomes vertical. The outer cylinder is filled with oil to thelevel line of 127 mm depth marked on the inner surface of the cylinder.

If Type A device having the clamp in the top of the inner cylinder isused, the inner cylinder is raised, held in a raised position with onehand, the test piece is clamped between clamping plates, then thecylinder is lowered, and allowed to float on the oil.

If Type B device is used, the inner cylinder is taken out, the testpiece is clamped, the inner cylinder is inserted into the outercylinder, the inner cylinder is gradually lowered, and allowed to floaton the oil.

When the device having the clamp in the base is used, first the innercylinder is raised until its top rim is supported by the catch, the testpiece is clamped between the clamping plates, then the inner cylinder isgently lowered until it floats. When the steady movement of the innercylinder has been attained, using a stopwatch or other timing device,the number of seconds required for the graduations from 0 to 100 ml topass the rim of the outer cylinder are measured. For very resistantpapers, the reading may be taken at the end of first 50 ml graduation,and the results doubled. For porous papers, the number of seconds for100 ml or over may be read, and converted to the 100 ml standard volume.

The test for at least five test pieces for each top side and back sideis performed, and the average of the results is taken. However, forheterogeneous papers, the test is performed for not less than 10 testpieces, and the average is taken by discarding extraordinary values.

In clamping the test piece, the inner cylinder is suspended with onehand, and the nuts alternately fastened so that the pressures on bothsides become equal to each other. Care should be taken not toexcessively fasten the nut on either side alone, or it can cause airleakage through the clamping plate and the test piece.

The average number of seconds required for the displacement of 100 ml ofair through the paper of an area of 645 mm² is taken as the airpermeability, and the value which is rounded to two significant digitsis reported.

In this case, when the bottom of the paper receptacle is heated (e.g.,when cooked at atmospheric temperatures of 200-250° C. for 10-20minutes), then the heat-resisting coating or the heat-resisting film maybe lifted and peel off from the paperboard.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a paper receptacle withcurling having increased strength, with reduced inferior heat sealingand with increased heat resistance.

Another object of the present invention is to provide a paperboardmaterial formed as the paper receptacle above, a method of forming thepaper receptacle above, and a machine for forming the paper receptacleabove.

To achieve the objects above, a first aspect of the present inventionrelates to a paperboard material for a paper receptacle at least havinga peripheral wall and having its outer periphery curled, which has aplurality of score lines impressed from the surface to the back side toextend approximately radially from a portion corresponding to theperipheral wall toward the outer periphery and to terminate inside theouter periphery at a certain distance therefrom.

A second aspect of the present invention relates to a paper receptacleformed only by press-forming from a sheet of paperboard material, whichincludes a bottom portion, a side wall portion connecting with thebottom portion, a flange portion connecting with the side wall portionand extending in a horizontal direction, and a curled portion formedaround the outer periphery of the flange portion, wherein the surface ofthe flange portion has smoothness which enables heat sealing.

According to a third aspect of the present invention, in the paperreceptacle of the second aspect of the present invention, a plurality ofscore lines are impressed on the paperboard material from the surface tothe back side to approximately radially extend toward the outerperiphery.

A fourth aspect of the present invention relates to a paper receptacleformed only by press-forming a sheet of paperboard material, wherein thepaperboard material has a multi-layered structure including a paperboardhaving a weight of 200 to 450 g/m², a density of 0.65 to 0.82, and a gaspermeability of 50 to 200 sec, a first resin layer formed on the entiresurface of the paperboard and having liquid-impermeability and thermalresistance, and a second resin layer formed on the entire back surfaceof the paperboard and having permeability to gas and liquid.

A fifth aspect of the present invention relates to a method for forminga paper receptacle in which a paperboard material composed of a sheetmaterial having an outer periphery of polygonal shape with a straightportion and a curved portion with rounded corners and having a pluralityof score lines impressed from the surface to the back side toapproximately radially extend toward the outer periphery in a portioncorresponding to the curved portion is formed into a paper receptacle,which includes the steps of: compacting a straight peripheral portioncorresponding to the straight portion in the outer peripheral portion ofthe paperboard material and a curved peripheral portion corresponding tothe curved portion in the outer peripheral portion of the paperboardmaterial in such a way that the straight peripheral portion has asmaller thickness than the curved peripheral portion, forcing thecompacted straight peripheral portion and curved peripheral portion intoa clearance narrower than the respective compacted thicknesses to ironand compress the straight peripheral portion and curved peripheralportion, and curling the compressed outer peripheral portion of thepaperboard material to form a curled portion.

A sixth aspect of the present invention relates to a machine for forminga paper receptacle having a bottom portion, a side wall portionconnecting with the bottom portion, a flange portion connecting with theside wall portion and extending in a horizontal direction, and a curledportion formed around the outer periphery of the flange portion, whichincludes: a pair of first and second die members for pressing apaperboard material interposed therebetween to form the bottom portion,the side wall portion and the flange portion, the first and second diemembers being so formed that the bottom portion and the side wallportion form, when being pressed, an angle smaller than thecorresponding angle of after being formed and the side wall portion andthe flange portion form an angle smaller than the corresponding angle ofafter being formed; a pair of first and second outer frame membersprovided respectively around, and corresponding to, the pair of diemembers so as to abut on each other while pressing; and a curl ringmember provided between the second die member and the second outer framemember so as to abut on the inner end of the abutting surface of thefirst outer frame member while pressing; wherein the inner end of theabutting surface of the first outer frame member and the abuttingsurface of the curl ring member have respective circular grooves facingeach other, the grooves having inner wall surfaces curved in the curlingdirection, the respective grooves being formed to constitute a curlinggroove when abutting; the inner end of the groove of the first outerframe member is formed so as to be located outside the inner end of thegroove of the curl ring member when abutting and to form such aclearance, with the inner wall surface of the groove of the curl ringmember, as can pinch and compact the edge of the outer peripheralportion of the paperboard material; the first die member and the firstouter frame member relatively move toward the second die member and thesecond outer frame member, whereby the paperboard material is heldbetween the pair of die members and the outer peripheral portion of thepaperboard is pressed and compacted between the pair of outer framemembers; and with the pair of die members holding the paperboardmaterial therebetween, the first outer frame member, the second outerframe member and the curl ring member, while abutting, relatively moveto the side of the second outer frame member, whereby the outerperipheral portion of the paperboard material is forced into a clearancebetween an inner peripheral surface of the first outer frame member andan outer peripheral surface of the second die member and ironed andcompressed; and when the edge of the outer peripheral portion of thepaperboard material is located at the inner end of the curling groove,only the curl ring member is caused to stop moving, whereby the edge ofthe outer peripheral portion of the paperboard material is pinched andcompacted between the inner end of the groove of the first outer framemember and the inner wall surface of the groove of the curl ring memberand the edge of the outer peripheral portion of the paperboard materialis set in the curling direction; and after setting the edge of the outerperipheral portion of the paperboard material in the curling direction,the first outer frame member, the second outer frame member and the curlring member are moved, while abutting, in the opposite direction, to theside of the first outer frame member, whereby the outer peripheralportion of the paperboard material is inserted into the curling grooveand curled along the inner wall surface of the curling groove, so as toform the curled portion.

According to a seventh aspect of the present invention, in the machinefor forming a paper receptacle of the sixth aspect of the presentinvention, the paper receptacle is a polygonal paper receptacle havingits outer periphery formed of a straight portion and a curved portion,and the first and second outer frame members are so formed that thepress thickness of a flange straight portion corresponding to thestraight portion in the portion forming the flange portion when pressingis smaller than the press thickness of a flange curved portioncorresponding to the curved portion in the portion forming the flangeportion.

As explained above, according to the paperboard material of the firstaspect of the present invention, the plurality of score lines do notreach the outer periphery of the paperboard material but terminate onthe inner side of the outer periphery at a certain distance awaytherefrom. Accordingly, when the outer peripheral portion of thepaperboard material is curled, the absence of the score lines at leastin part of the curled region increases the strength of the curl.

According to the paper receptacle of the second aspect of the presentinvention, the surface of the flange portion of the formed paperreceptacle has smoothness enough to allow heat sealing. Therefore, whenprotection film is heat sealed to the paper receptacle, the defectiverate of sealing can be reduced.

According to the paper receptacle of the third aspect of the presentinvention, in addition to the effect of the paper receptacle of thesecond aspect of the present invention, the plurality of score linesimpressed from the surface to the back side absorb corrugations takingplace on the inner side of the receptacle to give increased smoothnessto the surface.

According to the paper receptacle of the fourth aspect of the presentinvention, the paperboard material is of multi-layered structureincluding a paperboard, a first resin layer and a second resin layerhaving certain values of physical properties and characteristics. Thisprevents peeling off of the first resin layer from the paperboard due toheating when this paper receptacle is used as a heat-resistingreceptacle.

According to the method of forming a paper receptacle of the fifthaspect of the present invention, the outer peripheral portion of thepaperboard is so compacted, ironed and compressed that the straightperipheral portion is thinner than the curved peripheral portion, whichprevents buckling and breakage of the paperboard in forming.

According to the machine for forming a paper receptacle of the sixthaspect of the present invention, the first and second die members are soconstructed that the angle between the bottom portion and the side wallportion in pressing and the angle between the side wall portion and theflange portion are smaller than the corresponding angles of after theforming. Accordingly, even when forming a porous paperboard materiallacking firmness, high resistance is secured to deformation.

According to the machine for forming a paper receptacle of the seventhaspect of the present invention, in addition to the effect of theforming machine of the sixth aspect of the present invention, the firstand second outer frame members are so formed that the press thickness ofthe flange straight portion is smaller than the press thickness of theflange curved portion when pressing. This prevents buckling and breakageof the paperboard material when the paperboard material is compressed.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the left half of a paperboard materialaccording to a first embodiment of the present invention.

FIG. 2 is a diagram showing the cross-sectional structure of thepaperboard material in FIG. 1.

FIG. 3 is a diagram showing the cross-sectional structure of the scorelines formed in FIG. 1.

FIG. 4 is a diagram showing a cross-sectional structure of a machine forforming the paper receptacle according to the first embodiment of thepresent invention.

FIG. 5 is the enlarged cross-sectional view of "X" in FIG. 4.

FIG. 6 is the cross-sectional view along the line VI--VI in FIG. 5.

FIG. 7 is the cross-sectional view along the line VII--VII in FIG. 6.

FIG. 8 is an enlarged cross-sectional view of the main part of the firstdie member 21 and the first outer frame member 23 shown in FIG. 5.

FIG. 9 is an enlarged cross-sectional view of the main part of thesecond die member 22, the curl ring member 25 and the second outer framemember 24 shown in FIG. 5.

FIG. 10 is a diagram showing the change of the clearance between thefirst outer frame member 23 and the second die member 22 shown in FIG. 8and FIG. 9.

FIG. 11 is a cross-sectional view showing the forming machine shown inFIG. 4 with the paperboard material of FIG. 1 set therein.

FIG. 12 is a cross-sectional view showing the situation in which thefirst die member 21 and the first outer frame member 23 have beenlowered from the state shown in FIG. 11 to press the paperboard material101.

FIG. 13 is a diagram showing the situation in which the first outerframe member 23 has been further lowered from the state shown in FIG.12.

FIG. 14 is a diagram showing the situation in which the first outerframe member 23 has been further lowered from the state of FIG. 13 andthe top surface of the second outer frame member 24 coincides with thetop surface of the curl ring member 25.

FIG. 15 is a diagram showing the change of the form of the groove whenthe first outer frame member 23 is further lowered from the state shownin FIG. 14.

FIG. 16 is a diagram showing the situation in which the first outerframe member 23 has been raised from the states of FIG. 14 and FIG. 15and the curling has been formed around the outer periphery of thepaperboard material 101.

FIG. 17 is a diagram showing the change of shape of the score lines 117formed in the paperboard material 101 of FIG. 1 in the forming process.

FIG. 18 is a diagram showing the form of the paperboard material for acircular paper receptacle according to a second embodiment of thepresent invention.

FIG. 19 is a plan showing a paper receptacle formed by using thepaperboard material of FIG. 18.

FIG. 20 is a perspective view showing the form of a conventionalrectangular paper receptacle.

FIG. 21 is a diagram showing the form of the paperboard material for therectangular paper receptacle shown in FIG. 20.

FIG. 22 is a process diagram schematically showing the process offorming the paperboard material of FIG. 21 to produce the rectangularreceptacle of FIG. 20.

FIG. 23 is a cross-sectional structure diagram showing the rectangularpaper receptacle shown in FIG. 20 when used as a receptacle with acover.

FIG. 24 is a cross-sectional view showing a main part of the rectangularpaper receptacle of FIG. 20 with protection film heat sealed by usingthe flange portion 126.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a diagram showing the left half of a blanked paperboardmaterial for a rectangular formed receptacle according to a firstembodiment of the present invention, FIG. 2 is a diagram showing thestructure of a cross section of the paperboard material of FIG. 1, andFIG. 3 is a diagram showing a cross section of the score lines in FIG.1.

Referring to these diagrams, the paperboard material 101 is mainlycomposed of a white paperboard 161 with a thickness of 0.22 to 0.50 mm(weight: 200 to 450 g/m², density: 0.65 to 0.82, gas permeability: 50 to200 sec.) Formed or bonded on the inside of the receptacle is aheat-resisting resin coating layer or a heat-resisting resin film layer163 composed of polyester (thickness: 40 to 45 μm), polymethyl pentene(thickness: 25 to 30 μm), polycarbonate, or the like. Formed on theother side, the outside of the receptacle, is a thin resin coating layer165 having the slipping property and permeability to gas and liquid. Theshapes of the boundary 113 of the portion corresponding to the bottom123 designated by the dotted line and the portions corresponding to theperipheral walls 119 and 121 are the same as those of the paperboardmaterial of FIG. 21 shown in the conventional example.

The score lines 117 are formed in the fan-like areas A radially aroundthe centers of the curved portions, 115a and 115b, from the boundary113. Unlike the conventional example of FIG. 21, however, the scorelines 117 terminate on the inside of the edge of the paperboard material101 at a dimension "a" of about 1 to 3 mm, instead of extending to theedge. The score lines 117 are formed by pressing the paperboard material101 with a die from the inner side of the receptacle toward the outerside as shown in FIG. 3. The concave portions 117a of the score lines117 have a depth L₁ (0.1 to 0.3 mm) and a width W₁ (0.5 to 1.0 mm) andthe convex portions 117b have a depth L₂ (0.1 to 0.25 mm) and a width W₂(0.8 to 1.6 mm.)

FIG. 4 shows a cross-sectional structure of a machine for forming thepaperboard material shown in FIG. 1 to produce a paper receptacle.

Referring to the diagram, a first die member 21 and a second die member22 are provided as a pair of die members. A first outer frame member 23is provided around the first die member 21, which is attached to a baseportion 27 through a supporting plate 40. The lower end of the firstouter frame member 23 inwardly protrudes to form a stopper and the upperend of the first die member 21 outwardly protrudes to form a stopper.

These stoppers abut on each other so that the first die member 21 can besupported by the first outer frame member 23. Springs 29 and 30 areprovided between the first die member 21 and the base portion 27. Thesesprings 29 and 30 downwardly energize the first die member 21.

The second die member 22 is attached to a base portion 28 through asupporting plate 33. Provided around the second die member 22 is acircular curl ring member 25 having straight and curved portions on itsperiphery. Provided around the curl ring member 25 is a circular secondouter frame member 24. The curl ring member 25 and the second outerframe member 24 are both upwardly energized by springs 31 and 32.

The upper part of the second die member 22 outwardly protrudes to form astopper, which abuts on the stopper inwardly protruding in the lowerpart of the curl ring member 25 to position the curl ring member 25 bylimiting its upward movement.

The lower part of the curl ring member 25 outwardly protrudes to form astopper, which abuts on a stopper protruding in the upper part of thesecond outer frame member 24.

Provided around the second outer frame member 24 is a positioning ring34, which is upwardly energized by springs 35 and 36. The upwardmovement of the positioning ring 34 is limited by abutment of thestopper inwardly protruding in the lower part of the positioning ring 34and the stopper outwardly protruding in the upper part of the secondouter frame member 24.

The upper part of the positioning ring 34 is formed to upwardly protrudebeyond the second outer frame member 24 and the curl ring member 25.Pressing the upwardly protruding top part of the positioning ring 34against the energizing force of the springs 35 and 36 enables thepositioning ring 34 to downwardly move.

The lower parts of the springs 31 and 32 upwardly energizing the secondouter frame member 24 and the curl ring member 25 are located on thebase portion 28 through the holes formed in the supporting plate 33. Acircular stopper ring 39 is provided on each of the holes of thesupporting plate 33 through which the springs 31 and 32 pass, thesprings 31 and 32 passing through the holes formed in the stopper ring39.

The inner part of the stopper ring 39, which faces the curl ring member25, has a slightly raised step 39a. When the second outer frame member24 and the curl ring member 25 downwardly move against the energizingforce of the springs 31 and 32, the curl ring member 25 hits the step39a of the stopper ring 39 to stop. The lower end of the second outerframe member 24 and the stopper ring 39 are formed so as not to abut oneach other even at the bottom dead point.

Pins 41 and 42 are attached to the second outer frame member 24 inproper parts in its lower part. These pins 41 and 42 are passed throughengaging holes 43a and 44a of engaging plates 43 and 44, respectively.As the second outer frame member 24 moves up and down, the pins 41 and42 move up and down in the ranges of the engaging holes 43a and 44a.Accordingly, the positions of the top dead point and the bottom deadpoint of the second outer frame member 24 can be adjusted by adjustingthe relative positions of the engaging holes 43a and 44a and the pins 41and 42.

A band heater 38 is attached around the first outer frame member 23 anda band heater 37 is provided inside the second die member 22. The bandheater 37 may be provided on the exterior surface of the second diemember 22, instead of the inside of the second die member 22. Thesprings 35 and 36 for energizing the positioning ring 34 have a weakenergizing force. Therefore, when the first outer frame member 23 movesdown to abut on the second outer frame member 24 and the curl ringmember 25, they are compressed even with a slight force so that thefirst outer frame member 23 can abut on the second outer frame member 24and the curl ring member 25.

Although this diagram only shows the springs 35 and 36 on the right andleft sides, springs for energizing the positioning ring 34 are alsoprovided in other proper positions along the positioning ring 34.Similarly, not only the springs 31 and 32, but also other springs areprovided in other proper positions along the second outer frame member24 and the curl ring member 25 to energize the second outer frame member24 and the curl ring member 25. The same is true for the springs 29 and30 for energizing the first die member 21.

FIG. 5 provides an enlarged view of the part "X" in FIG. 4.

Referring to the diagram, a circular groove 26a is formed on the innerend of the abutting surface 23a of the first outer frame member 23. Aswell, a groove 26b is formed in the abutting surface of the curl ringmember 25, the groove 26b facing the groove 26a.

This diagram shows the first outer frame member 23 and the second outerframe member 24 and the curl ring member 25 abutting on each other. Thegrooves 26a and 26b are curved in the curl ring direction as shown inthe diagram, which form the curling groove 26 when abutting.

The radius of the groove 26a of the first outer frame member 23 isdifferent from the radius of the groove 26b of the curl ring member 25.That is to say, they are formed such that the groove 26a has a smallerradius than the groove 26b. As the result, the inner edge 26c of thegroove 26a is located outside the inner edge 26d of the groove 26b. Theclearance between the inner edge 26c of the groove 26a and the innerwall surface of the groove 26b is adjusted so that the inner edge 26cand the inner surface of the groove 26b can pinch and compact the edgeof the periphery of the paperboard material when they abut. Although thegrooves 26a and 26b in this embodiment have curved inner walls withoutirregularities, a large number of lateral grooves outwardly extendingfrom the inside may be formed on their inner walls.

The peripheral portions of the corners of the paperboard material areapt to be irregular with folds. The irregular peripheral portions of thepaperboard material are curled, guided by the lateral grooves, wheninserted into the curling groove. Accordingly, formation of such lateralgrooves enables curling with the folds uniformly distributed. In thisembodiment, however, in which the score lines 117 are formed in thecorners in advance, and with the effect of compacting the outerperiphery of the paperboard material, the folds can be uniformlydistributed and absorbed by the score lines 117 so that the paperboardmaterial can be smoothly curled, without the necessity of forming suchlateral grooves.

The parts for forming the bottom of the formed receptacle, that is, thebottom surface 21b of the first die member 21 and the top surface 22b ofthe second die member 22 are parallel to each other, but are bothinclined toward the center at θ₁ (about one to three deg) with respectto the horizontal plane. The reason for this is as follows: Thepaperboard material used in this embodiment is porous and lacksfirmness. Accordingly, the angle between the bottom and the side wallsof the receptacle is set smaller than the original angle to increase theresistance of the formed receptacle to deformation.

FIG. 6 is the cross-sectional view along the line VI--VI in FIG. 5,mainly showing a corner of the second outer frame member, and FIG. 7 isthe cross-sectional view along the line VII--VII in FIG. 6.

Referring to these figures, in the top surface of the second outer framemember 24, the surface 24a corresponding to a corner of the receptacleis formed lower than the surface 24b corresponding to a straight part ofthe receptacle. Specifically, the clearances T₁ and T₂ above thesurfaces 24a and 24b formed when the first outer frame member 23 abutson the positioning ring 34 are, if the paperboard material is 0.4 mmthick, set approximately as T₁ =0.3-0.35 mm, T₂ =0.2-0.3 mm.

The surface 24a of the second outer frame member 24 corresponding to acorner of the receptacle and the surface 24b corresponding to a straightportion of the receptacle are formed at different levels from each otherfor the reason given below.

In the case of a rectangular receptacle, when the peripheral portion ofthe paperboard material is compacted, folds take place, with the effectof the score lines formed in the corners of the paperboard. Accordingly,a large difference in thickness is caused between the corners and thestraight portions of the paperboard material. Therefore, if theclearance between the top surface of the second outer frame member andthe first outer frame member is uniform as in a conventional formingmachine, the portions corresponding to the corners are extremelycompressed, which will increase the possibility that the paper may bebroken in the compacting process. Even if the compacting process isfinished without problem, with the conventional machine, the peripheralportions of the straight portions are not sufficiently compacted ascompared with the corners, which may cause the curled parts of thestraight portions to buckle or to be insufficiently curled in thefollowing curling process, degrading the quality of the paperreceptacle.

FIG. 8 is an enlarged cross-sectional view showing the main part of thefirst die member 21 and the first outer frame member 23 of FIG. 5.

Referring to the drawing, the clearance between the outer peripheralsurface 21a of the first die member 21 and the inner peripheral surface23b of the first outer frame member 23 becomes wider as it goes down.The inner edge portion 26c of the groove 26 is formed below the innerperipheral surface 23b. The clearance d₁ between the inner peripheralsurface 23b and the outer peripheral surface 21a above the inner edge26c is, though it depends on the material of the paperboard in the partscorresponding to the straight portions, preferably about two-thirds toone-fourth of the thickness of the paperboard, and is usually aboutone-third. If the clearance d₁ is larger than two-thirds of thethickness of the paperboard, the peripheral portion of the paperboard isnot compacted sufficiently, causing difficulty in curling. If theclearance d₁ is smaller than one-fourth of the thickness of thepaperboard, the limit of compression of paper is exceeded, and then thepaper texture would be broken and torn, or the paper or the machinemight be damaged. The clearance corresponding to the corners of thereceptacle is equal to the clearance d₁ for the straight portionmultiplied by the above-described T₁ /T₂.

For the length, in the height direction, of the inclined surface of theinner wall surface 23b of the first outer frame member 23, the lengthnecessary for curling plus an allowance is required. If the curling hasa diameter of 3 mm, for example, it is preferable to set the length toabout 10 mm.

FIG. 9 is an enlarged cross-sectional view showing the main part of thesecond die member 22, the second outer frame member 24 and the curl ringmember 25 of FIG. 5.

The clearance between the outer peripheral surface 22a of the second diemember 22 and the inner peripheral surface 25a of the curl ring member25 becomes wider as it comes up, wherein the clearance d₂ in the widesttopmost part is preferably the same as the clearance d₁ between thefirst die member and the first outer frame member. While the innerperipheral surface 25a of the curl ring member 25 extends in thevertical direction, the outer peripheral surface 22a of the second diemember has an inclined surface which is inwardly inclined as it gets up.The length of this inclined surface in the height direction is equal tothe length necessary for curling plus an allowance, similarly to that ofthe inner peripheral surface 23b of the first outer frame member 23.Accordingly, if the curling has a diameter of 3 mm, it is about 12 mm.

The length 12 mm includes a winding allowance of about 3 mm for curling,which results from consideration of productivity of the paperreceptacles. That is to say, while winding a larger part strengthens thecurling, this increases the winding resistance, reducing theproductivity.

As shown in FIG. 8 and FIG. 9, the bottom surface 21c of the first diemember 21 on the side of the first outer frame member 23 and the topsurface 22c of the second die member 22 on the side of the curl ringmember 25 are parallel to each other, but these surfaces are inclinedtoward the inside at an angle θ₂ (about one to three deg) with respectto the horizontal plane. The purpose of this is to set the angle betweenthe flange and the peripheral walls of the receptacle smaller than theoriginal angle so that the formed receptacle can be highly resistant todeformation, for the paperboard material used in this embodiment lacksfirmness.

FIG. 10 is an enlarged cross-sectional view showing the situation inwhich the first outer frame member 23 downwardly moves to iron andcompress the peripheral portion of the paperboard in the clearancebetween the inner peripheral surface 23b of the first outer frame member23 and the outer peripheral surface 22a of the second die member 22.

In this diagram, the first outer frame member 23 has moved down to reachthe bottom dead point. In this situation, the clearance between theouter peripheral surface 22a and the inner peripheral surface 23b isequal to the above-described clearances d₁ and d₂. Accordingly, if thed₁ and d₂ are about one-third of the thickness of the paperboard, theclearance at the bottom dead point is about one-third of the thicknessof the paperboard.

In FIG. 10, the phantom line shows the first outer frame member 23 inthe course of the downward movement. As shown in this figure, theclearance between the inner peripheral surface 23b and the outerperipheral surface 22a is larger than the final clearance until thefirst outer frame member 23 reaches the bottom dead point. The clearancebecomes smaller as it approaches the bottom dead point, so that theouter peripheral portion of the paperboard material is gradually ironedand compressed. Hence, according to this embodiment, rapid ironing tothe outer peripheral portion of the paperboard material is avoided,which prevents seizure of the paperboard material onto the dies andbreakage of the paperboard material due to friction between thecontacting surfaces of the dies and the paperboard material.

Furthermore, since the inner peripheral surface 23b of the first outerframe member 23 and the outer peripheral surface 22a of the second diemember 22 are somewhat inclined with respect to the forming direction,the paperboard is pressed while being formed. This allows the paperboardto be more strongly compressed as compared with a machine whichvertically irons and compresses the paperboard, leading to easiercurling.

Provided next is the description of the process of forming a rectangularpaper receptacle with a curled periphery from the paperboard material ofFIG. 1 by using the forming machine shown in FIG. 4

First, as shown in FIG. 11, the paperboard material 101 is set on thesecond die member 22. At this time, the positioning ring 34 existsaround the paperboard material 101 to place the paperboard material 101in position.

Next, the first outer frame member 23 and the first die member 21 movedown. At this time, the first outer frame member 23 forcibly moves downto punch and compact the peripheral portion 101a of the paperboardmaterial 101 on the abutting surface of the second outer frame member24. The first outer frame member 23 hits the positioning ring 34 beforeabutting on the second outer frame member 24. However, the springs 35and 36 energizing the positioning ring 34 has so weak an energizingforce that the positioning ring 34 moves down with a slight force not tointerfere with the punching between the abutting surface of the firstouter frame member 21 and the second outer frame member 24.

The punching between the surface 23a of the first outer frame member 23and the surface 24a of the second outer frame member 24 compacts theperipheral portion 101a of the paperboard material 101 to increase itsdensity.

FIG. 12 is a cross-sectional view showing the situation where theperipheral portion of the paperboard material is compacted, which showsthe beginning of the process of pressing the paperboard material.

Referring to the diagram, the paperboard material 101 is pressed betweenthe first die member 21 and the second die member 22 and formed into acertain form. The peripheral portion 101a of the paperboard material 101is compacted between the first outer frame member 23 and the secondouter frame member 24 as stated above and hence it becomes more dense.The positioning ring 34 is pressed down by the first outer frame member23 and the springs 35 and 39 are in a compressed state.

In this state, when the base portion 27 further moves down, the springs29 and 30 are compressed. The force of the compressed springs 29 and 30serves to downwardly press the first die member 21, which furtherstrongly presses the paperboard material 101 with the second die member22. As the base portion 27 moves down, the first outer frame member 23moves to press down the curl ring member 25, the second outer framemember 24 and the positioning ring 34 together. This pressing forcecompresses the springs 31 and 32, and the curl ring member 25, thesecond outer frame member 24 and the positioning ring 34 move down.

FIG. 13 is a cross-sectional view showing the situation in which thecurl ring member 25, the second outer frame member 24 and thepositioning ring 34 are pressed by the first outer frame member 23 tomove down.

Referring to the diagram, as the first outer frame member 23, the curlring member 25, the second outer frame member 24 and the positioningring 34 move down together, the peripheral portion 101a of thepaperboard material 101 is forced into the clearance between the innerperipheral surface 23b of the first outer frame member 23 and the outerperipheral surface 22a of the second die member 22.

FIG. 13 shows the situation of immediately before the lower end of thecurl ring member 25 abuts on the step 39a on the inside of the stopperring 39. When the first outer frame member 23 further moves down, thecurl ring member 25 hits the step 39a of the stopper ring 39. Then itsmovement is limited and stopped, and the second outer frame member 24and the positioning ring 34 only move down.

FIG. 14 is a cross-sectional view showing this situation, where the curlring member 25 abuts on the step 39a of the stopper ring 39 and itsdownward movement is limited and stopped. The second outer frame member24, constructed not to abut on the outer lowered part of the stopperring 39, further moves down to reach the bottom dead point. Since thecurl ring member 25 is thus stopped and pressed earlier than the secondouter frame member 24, the inner edge 26c of the groove 26a of the firstouter frame member 23 pinches the edge of the peripheral portion 101a ofthe paperboard with the inner wall surface of the groove 26b andcompacts it. Since the inner wall surface of the groove 26b is curved,as the inner edge 26c compresses the peripheral portion 101a of thepaperboard material 101, its edge is bent and set in the curlingdirection. As the inner edge 26c of the groove 26a compacts the edge ofthe peripheral portion 101a of the paperboard material 101, the densityof the edge of the paper further increases. At the same time, thecurling set in the curling direction is formed on the edge as mentionedabove.

Next, the base portion 27 starts moving in the opposite direction, or inthe upward direction, and then the curl ring member 25, the second outerframe member 24 and the positioning ring 34, energized by the spring 31,move up together while abutting on the first outer frame member 23. Thismovement causes the peripheral portion 101a of the paperboard material101 to enter the curling groove 26. The peripheral portion 101a of thepaperboard material 101 inserted is curled along the curved inner wallin the curling groove to form the curling. At the same time, since theedge of the peripheral portion 101a, which has been compacted, has highdensity and is set in the curling direction, the peripheral portion 101aof the paperboard material 101 smoothly moves along the inner wallsurface of the curling groove 26 and is curled. Because the peripheralportion 101a of the paperboard material 101 has been compacted and hencehas high density, and the score lines do not extend to the edge, it isfirm enough to be smoothly curled without buckling in the curlinggroove. Since the curling is formed this way, the curled portion hasincreased strength.

FIG. 16 is a cross-sectional view showing the situation in which theperiphery of the paperboard material is curled.

Referring to the figure, after the pin 41 reaches the upper end of theengaging hole 43a and the upward movement of the second outer framemember 24 is limited and stopped, the positioning ring 34 moves up incontact with the first outer frame member 23 due to the energizing forceof the spring 35 to return to the initial position shown in FIG. 11. Thepaperboard material 101 has been pressed by the die members 21 and 22into a predetermined form, and the peripheral portion 101a of thepaperboard material 101 has been curled into the curling 127.

When the base portion 27 moves up to return to the position shown inFIG. 11, the formed rectangular receptacle with curling is removed fromthe second die member 22 and the next paperboard material is set for thenext forming process.

The machine of this embodiment serves as a longitudinal type pressingmachine with its center axis extending in the vertical direction, withthe first die member 21 positioned above and the second die member 22positioned below. In forming paper receptacles with curling, deviationbetween the die members is a serious problem and hence it is preferableto set the accuracy to 0.1 mm or smaller.

Dimension and shape, such as external diameter, of the curling can beappropriately selected depending on the size of the paper receptacle,the thickness of the paper, quality of the paper, etc. Consideringstrength of the paper receptacle, thickness of the paper receptacleswhen stacked, and so on, it is preferable to set the external diameterof the curling to about 1.5 to 5 mm.

FIG. 17 is a diagram for describing how the score lines 117 formed inthe paperboard material 101 of FIG. 1 change in the forming process.

Referring to these diagrams, as shown in FIG. 17(1), the thickness ofthe peripheral corner 125, before being formed, wherein the score lines117 are formed is taken as D₁. When the peripheral walls 119, 121, and125 are formed in this paperboard material 101, as shown in FIG. 22(2),the peripheral corner 125 is placed in a compressed state as it iscontracted due to formation of the plate-like peripheral walls 119 and121 on both sides. Then its thickness increases to D₂. In this state, asshown in FIG. 13, the first outer frame member 23 is lowered to form theupstanding portion 133. Then the upstanding portion 133 is ironed in theclearance between the inner peripheral surface 23b of the first outerframe member 23 and the outer peripheral surface 22a of the second diemember 22. As the result, as shown in FIG. 17(3), the convex portions117b of the score lines 117 on the outer side of the receptacle areformed into the folds 135 and the concave portions 117a of the scorelines 117 formed on the inner side of the receptacle are compressed fromboth sides to form the individual concave score lines 117c. Finally, inthe peripheral corner 125, as shown in FIG. 17(4), the inner side of thereceptacle is formed into a smooth surface wherein only the concavescore lines 117c are formed, and on the outer side of the receptacle,the folds 135 are flattened. Then it is curled as shown in FIG. 17(5).

When the paper is formed with the score lines 117 formed on the innerside of the receptacle, the score lines 117 thus absorb the folds in thecorners. Accordingly, the irregularities on the surface of the flange126 of the receptacle become very small, with the surface roughness of70 μm or smaller. This reduces inferior welding when protection film isheat-sealed to the flange 126.

In the portion corresponding to the curling 127, the score lines 117 arenot formed in the entire area as stated above. Therefore, fibers of thepaperboard material are partially prevented from being cut or brokenwhen the score lines 117 are formed and the concave score lines 117c inthe curling 127 are not formed so deep that the strength of the curling127 is reduced.

Although the paperboard material and the forming machine for rectangularreceptacles of quadrilateral shape have been described in the embodimentabove, the present invention is not limited to such rectangularreceptacles but can be applied to rectangular receptacles of polygonalshapes such as hexagon and octagon as well. That is to say, a polygonalsheet material having alternate straight lines and curves around itsperiphery with rounded corners shall be prepared as paperboard material.The score lines shall be formed in the peripheral wall portionscorresponding to the corners.

As to the forming machine, the individual parts shall be shapedcorresponding to the paperboard material formed of the polygonal sheetmaterial and the clearance for compacting the peripheral portion of thepaperboard material and the clearance for ironing and compressing theperipheral portion of the paperboard material can be determinedaccording to the conception given in the above-described embodiment.

FIG. 18 shows a paperboard material for a circular paper receptacleaccording to a second embodiment of the present invention and FIG. 19 isa plan of the circular paper receptacle formed by using the paperboardmaterial of FIG. 18.

Referring to these diagrams, the disk-like paperboard material 60 has aplurality of score lines 61 formed radially toward the periphery, thescore lines 61 being terminated at the position inside of the peripheryat a dimension b.

Forming the score lines 61 in this way increases the strength of thecurling 51 and provides desired smoothness for heat sealing in theflange 52, similarly to the case of the rectangular paper receptacle ofthe above-described embodiment.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

Industrial Applicability

As described on the above, the paper receptacle of the present inventionis adopted to be used as a simplified tableware in a shop providinglight meals and a camp, a party and the like out of doors, or as asimplified receptacle for foods in a supermarket and the like.

What is claimed is:
 1. A paper receptacle formed only by press-forming asheet of paperboard material, wherein said paperboard material has amulti-layered structure including,a paperboard having a weight of 200 to450 g/m², a density of 0.65 to 0.82, and a gas permeability of 50 to 200sec determined by measuring an average amount of time required to pass100 ml of air through an area of 645 mm² in the paperboard, a firstresin layer formed on the entire front surface of said paperboard andhaving liquid-impermeability and thermal resistance, and a second resinlayer formed on the entire back surface of said paperboard and havingpermeability to air and liquid.
 2. A paperboard material for a paperreceptacle at least having a peripheral wall and having its outerperiphery curled, which comprises:a plurality of score lines impressedfrom the surface to the back side to extend approximately radially froma portion corresponding to said peripheral wall toward the outerperiphery and to terminate inside said outer periphery at a distancebetween about 1 mm and about 3 mm therefrom, whereby when the paperreceptacle has its outer periphery curled, the score lines will be freeof any curling thereto.
 3. The paperboard material according to claim 2,wherein said distance is not more than the length of the portion to becurled to said outer periphery.
 4. The paperboard material according toclaim 3, wherein said paperboard material Is composed of a sheetmaterial of polygonal shape having rounded corners corresponding to apolygonal receptacle and said score lines are formed only in theperipheral wall portion corresponding to each of said corners.
 5. Thepaperboard material according to claim 2, wherein said paperboardmaterial is composed of a sheet material of polygonal shape havingrounded corners corresponding to a polygonal receptacle and said scorelines are formed only in the peripheral wall portion corresponding toeach of said corners.
 6. The paperboard material according to claim 2,wherein all of the score lines impressed in the paperboard materialterminate at the distance from the outer periphery of the paperboardmaterial.
 7. A method for forming a paper receptacle,comprising:preparing a paperboard material composed of a sheet materialhaving an outer periphery of a polygonal shape with a straight portion,and a curved portion having rounded corners; impressing a plurality ofscore lines from a surface of the paperboard material to a back side ofthe paperboard material to approximately radially extend toward theouter periphery in a portion corresponding to said curved portion, theimpressing terminating an end of the score lines at a distance betweenabout 1 mm and about 3 mm from the outer periphery; after saidimpressing, compacting a straight peripheral portion corresponding tosaid straight portion in the outer peripheral portion of said paperboardmaterials and a curved peripheral portion corresponding to said curvedportion in the outer peripheral portion of said paperboard material insuch a way that said straight peripheral portion has a smaller thicknessthan said curved peripheral portion; after said compacting, forcing saidcompacted straight peripheral portion and said curved peripheral portioninto a clearance narrower than the respective compacted thicknesses toiron and compress said straight peripheral portion and curved peripheralportion; and curling said compressed outer peripheral portion of saidpaperboard material to form a curled portion.
 8. A machine for forming apaper receptacle, the paper receptacle having a bottom portion, a sidewall portion connecting with said bottom portion, a flange portionconnecting with said side wall portion and extending in a horizontaldirection, and a curled portion formed around an outer periphery of saidflange portion, comprising;first and second die members for pressing apaperboard material interposed therebetween to form said bottom portion,said side wall portion and said flange portion, said first die memberand said second die member having respective surfaces facing each other,the surfaces having respective portions for forming the bottom portionof the paper receptacle, the respective portions being respectivelyangled toward a center of the respective die members and relative to ahorizontal plane, whereby when said bottom portion and said side wallportion are formed when being pressed, an angle defined therebetween issmaller than the corresponding angle after being formed first and secondouter frame members provided respectively around, and corresponding to,said first and second die members, said first and second outer framemembers abutting on each other while pressing; and a curl ring memberprovided between said second die member and said second outer framemember so as to abut on an inner end of an abutting surface of saidfirst outer frame member while pressing; wherein the inner end of theabutting surface of said first outer frame member and an abuttingsurface of said curl ring member have respective circular grooves facingeach other, said grooves having inner wall surfaces curved in a curlingdirection, said respective grooves being formed to constitute a curlinggroove when abutting, an inner edge of the groove of said first outerframe member is formed so as to be located outside an inner edge of thegroove of said curl ring member when abutting to form a clearance, withan inner wall surface of the groove of said curl ring member, as canpinch and compact the edge of the outer peripheral portion of saidpaperboard material, said first die member and said first outer framemember relatively move toward said second die member and said secondouter frame member, whereby said paperboard material is held betweensaid first and second die members and the outer peripheral portion ofsaid paperboard is pressed and compacted between said first and secondouter frame members, with said first and second die members holding thepaperboard material therebetween, said first outer frame member, saidsecond outer frame member and said curl ring member, while abutting, arerelatively moved to the side of said second die member, whereby theouter peripheral portion of said paperboard material is forced into aclearance between an inner peripheral surface of said first outer framemember and an outer peripheral surface of said second die member andironed and compressed, when the edge of the outer peripheral portion ofsaid paperboard material is located at the inner edge of said curlinggroove, only said curl ring member is caused to stop moving, whereby theedge of the outer peripheral portion of said paperboard material ispinched and compacted between the inner edge of the groove of said firstouter frame member and the inner wall surface of the groove of said curlring member and the curling set in the curling direction is formed onthe edge of the outer peripheral portion of said paperboard material,and after forming said curling set, said first outer frame member, saidsecond outer frame member and said curl ring member are moved, whileabutting, in the opposite direction, to the side of said first outerframe member, whereby the outer peripheral portion of said paperboardmaterial is inserted into said curling groove and curled along the innerwall surface of the curling groove, so as to form the curled portion. 9.The forming machine according to claim 8, wherein said paper receptacleis a polygonal paper receptacle having its outer periphery formed of astraight portion and a curved portion, and said first and second outerframe members are so formed that the press clearance of a flangestraight portion for forming said straight portion is smaller than thepress clearance of a flange curved portion for forming said curvedportion.
 10. The forming machine according to claim 9, wherein saidflange straight portion of said second outer frame member has a surfacethat is higher than the surface of said flange curved portion of saidsecond outer frame member.
 11. The forming machine of claim 8, whereinsaid second outer frame member has an upper surface facing the firstouter frame member, the upper surface having a first surface portiondisposed at a first distance away from the first outer frame member, anda second surface portion disposed at a second distance away from thefirst outer frame member, the second distance being greater than thefirst distance.
 12. The forming machine of claim 11, wherein the firstsurface portion and the second surface portion are disposed inessentially parallel planes.
 13. The forming machine of claim 12,wherein the first surface portion is disposed immediately adjacent tothe second surface portion so as to form a step arrangement.
 14. Theforming machine of claim 8, wherein the respective facing surfaces ofsaid first die member and said second die member have further portionsfor forming the flange portion of the paper receptacle, the respectivefurther portions being respectively angled toward the center of therespective due members and relative to the horizontal plane, wherebywhen said flange portion and said side wall portion are formed whenbeing pressed, an angle defined therebetween is smaller than thecorresponding angle after being formed.
 15. The forming machine of claim14, wherein the portions and the further portions of the respectivesurfaces are essentially planar.
 16. A method for forming a paperreceptacle, comprising:preparing a paperboard material composed of asheet material; impressing a plurality of score lines into a surface ofthe paperboard material to approximately radially extend toward an outerperiphery of the paperboard material, the impressing terminating an endof each of the score lines at a distance between about 1 mm and about 3mm from the outer periphery of said paperboard material; after saidimpressing, curling the outer periphery of said paperboard material toform a curled portion, whereby the score lines are free of any curlingthereto.